Low energy propellant producing essentially non reactive gaseous exhaust products

ABSTRACT

A NEW LOW ENERGY, DOUBLE BASE, COMPOSITE PROPELLANT COMPOSITION FOR USE AS A GAS GENERATOR CONTAINING CONVENTIONAL DOUBLE BASE COMPONENTS COUPLED WITH CERTAIN ACETATE ESTER PLASTICIZER, ARYL HYDROXIDE STABILIZERS, HETEROCYCLIC NITRAMINE CRYSTALLINE EXPLOSIVE FILLER, MODIFIERS AND CARBON BLACK, WHICH TOGETHER PRODUCE A LOW PRESSURE, MESA BURNING RATE CURVE AND ESSENTIALLY NONREACTIVE GASEOUS EXHAUST PRODUCTS.

Oct. 9, 1973 COSTA ET AL 3,764,41fi

LOW ENERGY PROPELLANT PRODUCING ESSENTIALLY NON-REACTIVE GASEOUS EXHAUST PRODUCTS Filed May 13, 1971 '7 Sheets-Sheet 1 LU U) E .2- LL! i.- 4 [Z (9 E 2 IP 5 0sl l l l I l l l l 2 3 4 s s 8 IO 3o PRESSURE, I00 PSI FIG. 1

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INVENTORS-' ROBERT LANTZ EDWARD COSTA WILLIAM O.SEALS 4 mam, 2441M 777.1% M

,qznm r Oct. 9, 1973 COSTA ET AL 3,764,416

LOW ENERGY PROPELLANT PRODUCING ESSENTIALLY NON-REACTIVE GASEOUS EXHAUST PRODUCTS Filed May 13, 1971 '7 Sheets-Sheet 2 5- |6OF 70F 2 .2 -40F Lu I- 1! E .1- 52 D .oa m

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INVENTORSI ROBERT LANTZ EDWARD COSTA WILLIAM O. SEALS Oct. 9, 1973 COSTA ET AL 3,764,416

LOW ENERGY PROPELLANT PRODUCING ESSENTIALLY NON-REACTIVE GASEOUS EXHAUST PRODUCTS Filed May 13, 1971 7 Sheets-Sheet 3 [60F g .3 70F 2 '1 40F w n: Z

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INVENTORS ROBERT LANTZ EDWARD COSTA WILLIAM O. SEALS m meys Oct. 9, 1973 COSTA ET AL 3,764,416

LOW ENERGY PROPELLANT PRODUCLNG ESSENTIALLY NON-REACTIVE GASEOUS EXHAUST PRODUCTS Filed May 15, 1971 7 Sheets-Sheet 1 3 70F 4 E V 40F LJ E O:

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.O6 05 J I l l l J l 2 3 4 5 6 8 IO 20 3O PRESSURE: I00 PSI INVENTORS ROBERT LANTZ EDWARD COSTA WILLIAM O. SEALS Get. 9, 1973 COSTA ET AL 3,764,416

LOW ENERGY PROPELLANT PRODUCING ESSENTIALLY NON-REACTIVE GASEOUS EXHAUST PRODUCTS Filed May 13, 1971 7 Sheets-Sheet 5 83 2. J m wzimzm PRESSURE, I00 PSI FIG.9

PRESSURE IOO PSI INVEN'T'URS.

ROBERT LANTZ FIG.|O

EDWARD COSTA BY: WILLIAM 0.3EALS 06$. 9, 1973 COSTA ET AL 3,764,416

LOW ENERGY PROPELLANT PRODUCING ESSENTIALLY NON-REACTIVE GASEOUS EXHAUST PRODUCTS Filed May 15, 1971 7 Sheets-Sheet 6 BURNING RATE, m/sEc 'N I l l I BURNING RATE, lN/SEC iv a 1 l l l I 2 3 4 5 e 8 I0 20 3o PRESSURE, [00 PSI FIG.|2

INVENTORS' ROBERT LANTZ EDWARD COSTA WILLIAM O. SEALS z ZZKYM Z M L M Oct. 9, 1973 COSTA ET AL 3,764,416

mw ENERGY PROPELLANI' PRODUCING ESSENTIAL-LY NON-REACTIVE GASEOUS EXHAUST PRODUCTS Filed May 13, 1971 7 Sheets-Sheet 7 m g S a E W Ns a T A0 If NLCO Mmmm l mm w y RE W 4 MM J 3 9m w 8mm 22:. N v fi o mwmE com 5% xzfi oom B 01 o E82 m2; w 009 12 EL 88 YES.

nited States 3 764,416 LOW ENERGY PROPELLANT PRODUCING ESSENTIALLY NON-REACTIVE GASEOUS EXHAUST PRODUCTS Edward Costa, Brooklyn, N.Y., and Robert Lantz, Chester, and William O. Seals, Budd Lake, N.J., assignors to the United States of America as represented by the Secretary of the Army Filed May 13, 1971, Ser. No. 143,275 Int. Cl. (10Gb 3/02 US. Cl. 14918 8 Claims ABSTRACT OF THE DISCLOSURE The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

BACKGROUND OF THE INVENTION This invention relates to a new low energy propellant composition having a low burning rate for a gas generator which by proper choice of components including aryl hydroxy compounds and heterocyclic nitramines produces gaseous exhaust products which are non-reactive towards certain widely used oxidizers, and in addition exhibits a low pressure, mesa burning rate vs. pressure curve. Generally, at a given temperature, the burning rate of a conventional propellant is directly related to the pressure to which it is exposed. This relationship can be expressed as: r=cp where r is the burning rate, p is the pressure and c and 11V are constants determined by the type of propellant used. Propellants exhibiting plateau and mesa effects deviate from the direct relationship over certain pressure ranges. If the exponent 11 exhibits a negative value the burning rate shows a decrease. This decrease in burning rate is called a mesa effect. If the exponent n is the burning rate remains constant and this ballistic property is called a plateau effect. If a logarithmic graph of burning rate vs. pressure for a particular propellant is prepared the mesa effect shows as a segment of negative slope on the curve, the plateau effect as a segment of zero slope. Propellants exhibiting a mesa effect give an actual decreased burning rate over a particular pressure range and as a result have a built in safety factor to insure against overpressurization of a container. The plateau effect results in a propellant with a constant thrust over the pressure range of the plateau.

Many propellant actuated devices are well known to the art and while initially developed for escape means from aircraft, have been used to advantage in any system requiring a short-duration high force application, for example, supplying gas pressure to operate hydraulic pumps in missiles, ejecting signalling devices from aircraft, jettisoning cargo from aircraft and ramming projectiles into the breech of large guns. These devices are generally simple, light, reliable and small. There are basically two types of these devices, short duration initiators and long duration gas generators. This invention is directed to providing a propellant composition for use in a gas generator.

Desirable characteristics for a gas generating composition include: a low heat of explosion value of about 900 3,764,418 Patented Oct. 9, 1973 ice cal./g. or less; a low burning rate, to achieve a long burn time; a temperature dependence of low magnitude to minimize pressure change at both high and low temperatures; a low flame temperature to minimize erosive effects on metal parts; a solids free exhaust, to prevent blocking of the exit orifice; good physical properties for ease of machining and handling; and a plateau or mesa effect to provide a built in safety factor and constant thrust.

In the past, solid, gas generator propellants have been used in a variety of devices, their use has been limited to mechanical force transfer mechanisms where the exhaust product impinges on a piston which then transfers the force generated to the liquid oxidizer or fuel, causing its expulsion into the reaction zone. This process is complex as it requires an intermediate mechanical step which introduces more weight into the item to be propelled and in addition requires the use of non-reactive pistons and special inert sealing rings. This intermediate step is inherently complex and therefore relatively unreliable. In addition it was difficult to produce a low pressure, plateau or mesa burning rate propellant containing an explosive crystalline filler, wiht the result that the item would be overpressurized by the time the plateau or mesa burning rate took effect thus negating the prime reason for producing this effect. Also, the solid propellant to generate the gas must be chosen primarily according to ballistic properties which are appropriate for operating pressure, environmental storage and use conditions. Consideration must be given to the criteria of reliability of ignition, smoothness of burning and wide temperature range stability. In addition any excess gas must be clean to minimize signature. Further, the interaction between the pressurizing gas and the article to be propelled such as heat transfer, mass transfer, and chemical reaction must be considered, yet it is difiicult to predict accurately. Chloride trifluoride-mixed hydrazine systems of propulsion are extremely sensitive to the above listed factors.

It is, therefore, an object of this invention to provide a new composition which has mesa and plateau ballistic characteristics at relatively low pressures and which has a low burning rate.

A further object is to provide a new composition with gaseous reaction products which are unreactive towards certain widely used rocket propellant oxidizers.

A still further object is to provide a propellant composition utilizing a high density, high nitrogen crystalline explosive filler in conjunction with a double base propellant which exhibits mesa ballistic burning rate versus pressure relationships.

Yet another object is to provide a lightweight, reliable, economical method of expulsion for rocket propellant oxidizers.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following detailed description.

These objects are attained and the prior art deficiencies are overcome by the addition of selected heterocyclic nitramine explosive fillers and aryl hydroxy compounds as stabilizers together with certain acetate ester plasticizers to a conventional ballistically modified double base propellant. The novel propellant exhibits a smooth, low burning rate and produces gaseous exhaust products which are free from particulate matter and which are nonreactive when contacted by chlorine trifluoride, thereby eliminating the necessity of a heavy, complex method of transmitting force to the oxidizer to be expelled. In addition the mesa or plateau burning rate vs. pressure curve is produced at pressures low enough to be useful as a safety factor in low pressure applications.

This advance in the art, herein described, is quite unexpected and forms, in effect, the basis of a discovery. The production of a low energy propellant exhibiting mesa ballistic characteristics that produce essentially unreactive gaseous exhaust products according to this invention is a major technological advance in the field of low energy propellants. Additionally, the composition is unique in that it contains a high density, high nitrogen crystalline explosive filler useful for good physical handling characteristics and yet exhibits plateau or mesa ballistics in a pressure range suitable for this application. Heretofore, the use of other explosive fillers, destroyed these effects.

The eifects of this invention are numerous. It provides a composition which exhibits mesa ballistics at pressures less than 1500 p.s.i. It provides a composition which has exhaust gas reaction products that are essentially nonreactive to liquid rocket propellant oxidizers. Further, this composition with its non-reactive exhaust products permits a Weight saving in rockets as it eliminates the need for a mechanical means of energy transfer to a liquid rocket propellant oxidizer. The gas used to push the oxidizer into the reaction zone of the rocket can safely impinge directly on the oxidizer. It facilitates use of a simpler, more reliable rocket structure, increases the available volume for fuels and eliminates the problem of misalignment inherent in many mechanical devices. In addition this composition allows the incorporation of crystalline fillers into a double base composition with retention of mesa ballistics.

The following range of compositions can be used to prepare the propellants of our invention:

In general, the procedure used for preparing our novel propellants is conventional and includes:

(1) Mixing the ingredients with the required amount and type of solvent to achieve proper colloidization;

(2) Preparing the colloided propellant for extrusion;

(3) Extruding the prepared propellant; and

(4) Curing the extruded propellant to a maximum volatile content of about 0.4% by weight.

More specifically, the propellant composition of our invention can be formulated in the following manner:

Dehydrated nitrocellulose, stabilizer, plasticizer and carbon black are blended together for about 30' minutes in a sigma blade mixer. The ballistic modifier is added and blended for about 15 minutes. The crystalline explosive filler, wet with alcohol, is added and blended for 15 minutes. Nitroglycerin, any remaining plasticizer and the balance of any solvents necessary to effectuate homogeneous mixing are then added and mixed in for about 60 minutes or until properly colloided. The mixer temperature is maintained at 40:5 F. throughout the mixing cycle. The colloided propellant is then screened, dried, extruded and cured in the conventional manner, then finally extruded and machined to the final design dimensions desired. Sarnple grains obtained in the above process are then tested. The plasticizers used in this invention are selected from the group of acetate ester plasticizers consisting of triacetin or sucrose octaacetate, either alone, in mixtures 01', in combination with other conventional fuel type plasticizers, such as the sebacate, adipate and phthalate esters or the like. If less than by weight is used, the physical characteristics of the propellant are impaired; if more than 25% by weight is used, the ballistics are lost.

Preferably in our invention the total weight percent of plasticizer is between about 12% by weight and about 17% by weight. A composition containing this amount of plasticizer will have better physical handling characteris tics with proper retention of ballistic properties and retain its smooth burning characteristics.

The ballistic modifiers that can be used to advantage are organic lead salts, such as lead malonate, lead malate, lead tartrate, lead cyclopentane carboxylate, lead stearate and the like, and mixtures thereof. Generally lead salts with larger organic moieties such as lead stearate are preferred. The amount of modifier that can be used is from about 1 to about 8% by weight depending on the modification desired; at less than 1% there is negligible modification and above 8% the mesa or plateau is lost. Preferably from about 2% to about 5% and particularly from about 2.5 to about 3.5% by weight is used to achieve proper modification.

The presence of carbon black is critical, the amount thereof can be varied from about 0.02 to 0.10% by weight to alter the burning rate, generally the higher percentages produce a faster rate.

The crystalline explosive fillers used to advantage can be any heterocyclic nitramine such as HMX (cyclotetramethylene tetranitramine), RDX (cyclotrimethylenetrinitramine), 1,3-dinitroimidoledone-2, and 1,3,5-trinitro-1,3, 5-triazacycloheptane. These fillers can be used alone or in admixture with each other in any proportion. It has further been found that the use of straight chain nitramines such as nitroguanidine, and 1,9-diacetoxypentamethylene tetra nitramine as well as other explosive fillers such as tetryl, TNT, diaminotrinitrobenzene and trinitromelamine produce only straight line ballistics. The amount of cyclic nitramine that may be used with our invention is from about 10 to about 30% by weight to achieve a ballistic modifying effect; preferably from about 20 to about 28% by weight and especially from about 23 to 26% by weight is used to achieve an optimum balance of physical handling characteristics, e.g. machinability, dimensional stability, for a low burning rate, low pressure mesa or plateau effect and production of non-reactive exhaust gases. If the outside limits of these percentages are substantially exceeded then either the physical characteristics or burning rate become disadvantageous.

The stabilizers used with our invention may be any aryl hydroxy compound including esters derived from aryl hydroxy compounds such as resorcinol, phloroglucinol, orcinol, o-hydroxy benzyl alcohol, 2,4-dinitroresorcinol, resorcinol diacetate, resorcinol monobenzoate, resorcinol dibenzoate, 2,3-dihydroxynaphthalene, 2-hydroxybiphenyl, pyrogallol triacetate, 4-hydroxybiphenyl, p-hydroxydiphenylamine, 1,4,9,10-tetrahydroxyanthrancene, 1,3 -dihydroxynaphthalene, 1,S-dihydroxynaphthalene, and resorcinol monoacetate. These stabilizers may be present in an amount of from about 1.0% to 5% by weight. If less than 1.0% is added the low pressure mesa is lost, if more than 5% is added again the mesa is lost. Preferably in our invention about 2 to 4% by weight is added to insure proper placement of the mesa effect on the pressure vs. burning rate curve. Proper selection of the compound and the amount of it to be used as a stabilizer depends upon the pressure at which the mesa effect is desired. For example, resorcinol monoacetate with the proper choice of other components shows plateau and mesa ballistics in the range of 750 to 1000 p.s.i. and orcinol shows plateau and mesa ballistics from 700 to 1500 p.s.i.

The composition of this invention, which may be used to produce a propellant having the properties desired, is set forth in the following examples:

EXAMPLE 1 114 pounds of nitrocellulose (12.6% N) was treated with ethyl alcohol to remove any water. The dehydrated nitrocellulose was added to a sigma blade mixer. Mixing 8, 10 and 11 show the effect of varying the concentration of crystalline filler. FIG. 12 shows the pressure vs. burning rate curve of a composition using a straight chain nitramine compound as a crystalline filter with a conventional stabilizer. FIG. 13 illustrates the temperature time relationship when the exhaust products of the composition of Example 1 impinge on the surface of chlorine trifluoride contained in a tank. FIG. 14 shows the pressure vs. time relationship in the above-mentioned tank.

The ballistic modification of the compositions specified 1n Examples 1 through 12 can be seen from the curves in FIGS. 1 through 12. A pronounced mesa effect is apparent in FIGS. 1 through 5 and 9. This mesa is shifted to lower pressure ranges by a proper combination of components The burning rate can also be shifted from high to low at a particular pressure range by a proper choice of components and in addition it has been found that a change 1n the percent of carbon black added produces a change in the burning rate. FIG. 6 shows a more gradual mesa, this is due to the nature of the stabilizer. FIG. 7 shows a plateau at the higher temperature, again this is due to the nature of the stabilizer. FIG. 8 containing 10% by weight crystalline filler shows a mesa eflect but this amount of filler is approaching the limits of usefulness. The reason a crystalline filler is useful is for ease of handling and at this low level the dimensional stability imparted by the addition of a filler is marginal. FIGS. 10 and 11 show the effect of higher percentages of crystalline filler and although there is a more gradual slope over the pressure range 600 p.s.i. to 800 p.s.i. there is neither a mesa nor aplateau effect. FIG. 12 shows the effect of a linear nitramine when used as a crystalline filler, there is no change exhibited in the burning rate. The small variation of the burning rate of all of the compositions is apparent from all of the curves presented. The low burning rate can be observed in most of the figures.

Generally a low calculated heat of explosion is indicative of a low energy propellant. In all of the cases 870 cal./gm. or less is considered low. The composition is composed of high energy ingredients and low energy ingredients and usually a balancing is necessary to achieve a particular energy level. For example, if the crystalline filler content is increased the quantity of some other high energy component such as nitroglycerin must be decreased. Certain limits exist within which the composition can be varied. Selection of the proper components is largely empirical and depends on desirable design conditions within the limits prescribed by our invention.

FIGS. 13 and 14 show the result of tests run using the composition of Example 1 to expel chlorine trifluoride from a tank.

The test apparatus used was a compartmental stainless steel cylinder approximately 70 inches long. The gas generator grain was formulated from the composition of Example 1 and placed in one of the compartments. The cylinder was vertically supported. A Teflon disc rated at 500 p.s.i. burst pressure was inserted in the ullage space between the gas generator and the chlorine tri-fiuoride (CTF) compartment. A perforated plate was inserted next to the Teflon disc to control gas flow. The exit diameter of the expulsion line from the CTF compartment was fixed at 0.472". A 200 p.s.i. stainless steel burst disc was placed in the expulsion line. Approximately 90 pounds of CTP was charged into the CTF space. The gas flow began with ignition and rupture of the Teflon disc, expulsion then took place after rupture of the stainless steel disc. Results of some of the measurements made are included in FIGS. 13 and 14. The lack of any sharp, sustained temperature or pressure rise is indicative of the non-reactivity of the gaseous exhaust product on the chlorine trifluoride. The exhaust product and flame temperature of this composition have been ascertained by the Hirschfelder-Sherman calculation published in NDRC A-101, OSRD 935 October 1942. The theoretical composition and flame temperature are presented in Table III.

8 TABLE III Gas composition exhaust at 14.7 p.s.i.

Product: Mole percent N 13.82 H 23.01 CO 8.38 CO 42.70 H O 12.01 Unoxidized C 9.30 Flame temperature K.) 2433 A low flame temperature is important because it minimizes erosion of metal parts.

We wish it to be understood that we do not desire to be limited to the exact detailsshown and described, for obvious modification will occur to a person skilled in the art.

We claim:

1. A propellant composition consisting essentially of colloided nitrocellulose, nitroglycerin, acetate ester type plasticizer of the group consisting of triacetin and sucrose 'octaacetate, ballistic modifier, carbon black, heterocyclic nitramine crystalline explosive filler and aryl hydroxide stabilizer, said propellant having a heat of explosion of 900 cal./gram or less, a maximum burning rate of 0.4 inch/ second below 1500 p.s.i., mesa ballistic characteristics over selected pressure ranges between about 500 p.s.i. and 2500 p.s.i. and gaseous exhaust products which are nonreactive with liquid rocket propellant oxidizer.

2. A propellant composition consisting of:

3. A composition as defined in claim 2 wherein said plasticizer is a mixture of an acetate ester type plasticizer selected from the group consisting of triacetin and sucrose octaacetate and a fuel type plasticizer selected from the group consisting of sebacate, adipate and phthalate esters.

4. A composition as defined in claim 2 wherein said heterocyclic nitramine crystalline explosive filler is selected from the group consisting of cyclotetramethylene tetranitramine, cyclotrimethylene trinitramine, 1,3-dinitroimidoledone 2, 1,3,5 trinitro 'l,3,5-triazacycloheptane and mixtures thereof.

5. A composition as defined in claim 2 wherein said aryl hydroxide stabilizer is selected from the group consisting of resorcinol, phloroglucinol, orcinol, o-hydroxy benzyl alcohol 2,4-dinitroresorcinol, resorcinol monoacetate, resorcinol diacetate, resorcinol monobenzoate, resorcinol dibenzoate, 2,3 dihydroxynaphthalene, 1,5- dihydroxynaphthalene, 1,3 dihydroxynaphthalene 2- hydroxybiphenyl, pyrogallol triacetate, 4 hydroxybiphenyl, p-hydroxydiphenylamine, 1,4,9,10-tetrahydroxyanthracene.

6. A composition as defined in claim 2 wherein said nitrocellulose having a N content of 12.6% by weight is present in an amount of 38% by weight; said nitroglycerin is present in an amount of 18.9% by weight; said heterocyclic nitramine explosive filler is cyclotetramethylene tetranitramine present in the amount of 25% by weight; said plasticizer is a mixture of triacetin present in the amount of 9.1% by weight and sucrose octaacetate present in the amount of 7.0% by weight; said aryl hydroxide stabilizer is resorcinol monoacetate present in the 10 References Cited UNITED STATES PATENTS 3,037,247 6/1962 Preckel 149-98 X 3,186,882 6/1965 Von Holt 149-98 X 3,379,588 4/1968 Corsi et a1. 149-98 STEPHEN J. LECHERT, 111., Primary Examiner US. Cl. X.R. 10 l4992, 98 

